Researchers from the University of California at San Diego analyzed 15 studies of nearly 761,000 people to get a handle on whether or not prediabetes increases stroke risk.

And it does -- sometimes. Stroke risk varies based on the definition of prediabetes. Not all studies in the new analysis defined prediabetes in the same way.

Prediabetes is typically defined as a fasting (not eating for 12 hours) glucose level between 100 to 125 mg/dl. Seventy to 100 mg/dl is normal.

Studies with people whose blood sugar levels were in the 110 to 125 mg/dl range showed a 21% greater likelihood of stroke. This risk held even after the research team took into account other factors that are known to increase risk for stroke.

This range was how the American Diabetes Association defined prediabetes in 1997. They changed the definition to 100mg/dl to 125mg/dl in 2003.

Studies that used the less-restrictive range did show a higher risk for stroke.

Future stroke risk begins to rise at or above a fasting glucose level of 110 mg/dL, the study authors suggest. Their findings appear in the British Medical Journal.

If you fall into this category, "the best thing you can do is alter your lifestyle," says researcher Bruce Ovbiagele, MD. He is a neuroscientist at University of California at San Diego. "Maintain a normal weight and try to exercise at least three times a week."

There is no medicine that treats prediabetes, but "lifestyle modifications can prevent more than 50% of people from going from prediabetes to frank diabetes, which is a major risk factor for stroke," he says.

The best part is that these lifestyle changes are side-effect free.

"There is a growing epidemic of prediabetes, and more people should check whether or not they have it, regardless of the difference in definitions," Ovbiagele tells WebMD.

Lifestyle Changes Can Prevent Full-Blown Diabetes

Minisha Sood, MD, agrees. She says prediabetes can be an important warning sign for future health problems, including stroke. Sood is an endocrinologist at Lenox Hill Hospital in New York City.

The question becomes: What can you do about it? "If someone has impaired fasting glucose, I suggest lifestyle modifications endorsing 5% to 10% weight loss if they are overweight or obese, 150 minutes of exercise per week, and counseling about how to accomplish this."

"Many people don't take complications of their disease to heart, and they don't put a lot of weight on lifestyle changes," she says. "The onus is on the patient, but physicians can't be lackadaisical about prediabetes either. ... Know your numbers so you can get a head start on reducing your cardiovascular risk factors."